The present invention relates to a mounting assembly for a ring-shaped deflection yoke surrounding the neck of a cathode-ray tube and expanding toward the screen like a trumpet, with a mounting part provided at the narrower end opening of the deflection yoke and movable on the tube neck and capable of being inclined toward the tube axis, and a supporting part provided at the expanding end opening of the deflection yoke.
Accurate positioning of the deflection plane relative to the electron-gun system and the screen is required, for example, in a cathode-ray color picture tube working on the shadow-mask principle. In such a tube, on the one hand, convergence of the electron beams is to be achieved in the area of the shadow mask, and, on the other hand, stringent requirements are imposed on the angles of incidence of the electron beams on the shadow mask and on the screen to insure that each beam hits only the phosphor dot element it is meant to strike.
During the manufacture of such a tube, inaccuracies are likely to occur which might lead to an undue degradation of picture quality. These inaccuracies are compensated for, to a certain degree, by subsequent adjustment of the deflection yoke.
To do this, the deflection yoke should be movable along and about the tube axis, and its inclination to the tube axis should be capable of being changed.
German Printed Patent Application (DE-AS) No. 2,224,702 discloses such an adjustable mounting assembly for a deflection yoke in which the yoke is held on one side from the front and in which, following adjustment, the elements designed to connect the yoke with the tube are surrounded with adhesives. Such an assembly has the disadvantage that the yoke must be held in position until the adhesive has hardened. In addition, the one-sided mounting of the yoke requires relatively heavy mounting parts. Thirdly, such a joint is difficult to separate if readjustment of the yoke becomes necessary. The same reference shows a second, similar assembly in which the yoke is locked in position by means of screws. This eliminates the need to wait for the adhesive to harden, and readjustment is possible without difficulty, but there is still the relatively heavy design because of the one-sided mounting of the deflection yoke. In addition, for automatic production, in which the yoke is adjusted by means of a device acting on the yoke directly from outside and moving it, that second assembly is unsuitable because it will be difficult to automatically lock these screws so that the setting found will not be changed again, because there are forces acting against the setting.
Another assembly is known from German Published Patent Application (DE-OS) No. 2,558,353 in which the deflection yoke is held from the front by means of spring arms projecting over the yoke. While not having the last-mentioned disadvantage, this assembly, because of the spring arms projecting over the yoke on one side only and acting on the yoke from outside at particular points only, must be of very heavy design which, in addition, hardly permits subsequent readjustment because the spring arms must be bonded or welded to the yoke.
An apparently more advantageous assembly is disclosed in German Published Patent Application (DE-OS) No. 2,445,577, in which the deflection yoke is supported by the rear, narrow end of the tube neck, while in front a spherical surface permits the yoke to be swivelled about its rear end, and additional rings fitted together also allow axial movement. This assembly has the disadvantage of requiring a large number of parts at the front end of the yoke which must also be relatively rugged because of their multitude and of the need to absorb forces exerted by the yoke in all directions.
An assembly known from German Published Patent Application No. 2,656,829 appears much simpler in construction. Here, the deflection yoke is mounted at the rear end so as to be axially movable and capable of being swivelled relative to the tube axis because of the elasticity of the mounting, while the front end of the yoke is supported by the tube via adjustable, screw-shaped legs. However, this assembly has the disadvantage mentioned last for the second arrangement of the above-cited DE-AS No. 2,224,702, namely that in case of automatic adjustment by means of a device acting from outside, the setting found is likely to be changed by the tightening of the screw-shaped supporting legs.
As assembly which appears to be free from this disadvantage is disclosed in German Published Patent Application No. 2,730,544. Here, the deflection yoke can be swivelled and is axially movable by being held in front in a ring mounted on the tube cone, while the rear end of the yoke, following adjustment, is screwed to an inclinable plate movable on the tube neck. Since the swivel point of the deflection yoke lies at the front end, a larger rear opening of the deflection yoke is necessary to obtain a sufficient swivel angle. This, in turn, decreases the electric deflection sensitivity of the deflection coils, which can only be compensated for by increased electric power.